The HAL HF-24 Marut ("Spirit of the Tempest") was an Indian fighter-bomberaircraft of the 1960s. It was developed by Hindustan Aircraft Limited (HAL), German aircraft designer Kurt Tank was responsible for being the lead designer of the aircraft. The Marut holds the distinction of being the first Indian developed jet aircraft, and also being the first Asian jet fighter to go beyond prototype/test phase, and into successful production and active service (outside Russia/Soviet Union). On 17 June 1961, the type conducted its maiden flight; on 1 April 1967, the first production Marut was officially delivered to the IAF.

While the Marut had been envisioned as a supersonic-capable combat aircraft, it would never manage to breach the sound barrier, being limited to subsonic speeds only. This limitation was principally due to the engines used, which in turn had been limited by various political and economic factors, multiple attempts to develop improved engines or to source alternative powerplants were fruitless. Criticism of the Marut's cost and lack of capability in comparison to contemporary aircraft were often made.

A total of 147 Maruts were manufactured, the majority of which were introduced to service with the Indian Air Force (IAF). While it had been initially envisioned as a capable interceptor aircraft, it was primarily used for ground attack missions instead. In the ground attack role, the Marut saw active combat operations during the Indo-Pakistani War of 1971, notably participating in the Battle of Longewala. By 1982, the Marut was increasingly considered to be obsolete, and was gradually phased out during the late 1980s.

During the 1950s, Hindustan Aircraft Limited (HAL) had developed and produced several types of trainer aircraft, such as the HAL HT-2. However, elements within the firm were eager to expand into the then-new realm of supersonicfighter aircraft.[2] Around the same time the Indian Government was in the process of formulating a new Air Staff Requirement for a Mach 2-capable combat aircraft to equip the Indian Air Force (IAF).[3] However, as HAL lacked the necessary experience in both developing and manufacturing frontline combat fighters, it was clear that external guidance would be invaluable; this assistance was embodied by Kurt Tank, a German aircraft designer who had designed numerous combat aircraft for the Luftwaffe while at Focke-Wulf during the Second World War.[4] Kurt was invited to relocate to India to establish and head the project to produce what would become India's first indigenous fighter aircraft. Upon arrival, he set about directing design work for the prospective fighter.[2][3][5]

In 1956, HAL formally began design work on the supersonic fighter project.[4][2] The Indian Government, led by Jawaharlal Nehru, authorised the development of the aircraft, stating that it would aid in the development of a modern aircraft industry in India.[6] The first phase of the project sought to develop an airframe that would be suitable for travelling at supersonic speeds, and could effectively perform combat missions as a fighter aircraft, while the second phase sought to design and assemble a domestically produced engine capable of propelling the type.[4] Early on, there was an explicit adherence to satisfying the IAF's requirements for a capable fighter bomber; attributes such as a twin-engine configuration and a 1.4/1.5 Mach number were quickly emphasised.[4]

During the development phase, HAL designed and constructed a full-scale two-seat wooden glider to act as a flying demonstrator. Designated as the HAL X-241, the glider replicated the subsequent production aircraft in terms of dimensions, control configuration and aerofoil sections. The wheel-brakes, air-brakes, flaps and retractable undercarriage were all actuated using compressed gas, there was sufficient gas storage on board to perform multiple actuations per flight.[7] On 3 April 1959, the X-241 flew for the first time, having been launched by aero-tow behind a Douglas Dakota Mk.IV BJ 449. A total of 86 flights were conducted prior to the X-241 receiving considerable damage as the result of a landing accident during which the nose undercarriage had failed to extend.[7][5]

On 24 June 1961, the first prototype Marut conducted its maiden flight.[3][5] It was powered by the same Bristol Siddeley Orpheus 703turbojet engines that had powered the Folland Gnat, which was also being manufactured by HAL at that time. On 1 April 1967, the first production aircraft was officially delivered to the IAF.[5] While originally intended only as an interim measure during testing, HAL decided to power production models of the Marut with a pair of unreheated Orpheus 703 engines, whose use meant the aircraft could not attain supersonic speeds.[3] Although it had been originally conceived to operate around Mach 2, the Marut in fact turned out to be barely capable of reaching Mach 1 due to the lack of suitably powerful engines for the airframe.[3][8]

The IAF were reluctant to procure a fighter aircraft that was only marginally superior to its existing fleet of British-built Hawker Hunter fighters; however, in 1961, the Indian Government decided to procure 16 pre-production aircraft and 60 series production Maruts as well.[5] Only 147 aircraft, including 18 two-seat trainers, were completed out of an initial target of 214 aircraft.[3] After the Indian Government conducted its first nuclear tests at Pokhran, international pressure prevented the import of better engines, or at times, even spares for the Orpheus engines used; this situation was one of the main reasons for the aircraft's early demise. The Marut had never realised its full potential due to insufficient power. According to author Amit Gupta, the Marut "was technically obsolete by the time it was first delivered in 1964".[3] Other authors have also commented on the Marut's relative obsolesce by the time it had reached production.[9]

According to aviation author Chris Smith, the Marut was "essentially a very long-drawn-out failure," he attributes the aircraft's shortcomings to multiple factors.[10] Amongst these were the difficulties experienced in securing a suitable engine, which was principally a political issue; while arrangements were successfully established with the United Kingdom and Bristol Siddeley to domestically produce the Orpheus engine by HAL, this engine was only suitable as an interim measure as it lacked the power to enable the Marut to achieve supersonic flight.[11] The Indian Government had refused a proposal made by Rolls-Royce to finance further development of the Orpheus, which had been specifically aimed at producing a more suitable model of the engine for the Marut.[11][3]

Other envisioned alternative engines that could have potentially been sourced from the Soviet Union, Egypt and various European nations did not result in anything of substance.[3][12] The Gas Turbine Research Establishment also perused their own development program to improve the Orpheus without external aid, which proceeded to the testing phase with some favourable results, but proved to be incompatible with the Marut.[13] As the particularities of a given airframe are typically heavily dependent on the engine used, the inability to develop the Marut around a specific engine damaged its performance.[12] Despite experimentation with various engines, the Marut was never able to achieve supersonic speeds, which was viewed as a major failure of a project which at one point had ambitions to produce a Mach 2-capable combat aircraft.[4] The IAF had anticipated the Marut being fitted with a considerably superior engine.[13][14]

The project was negatively affected by a lack of direction and management from the Indian Ministry of Defence.[12] A lack of coordination between the military, politicians, and industry is alleged to have been typical throughout the entirety of the programme, leaving many issues down to industry alone without guidance. Specifically, the government never sanctioned the development of an engine design team, nor were there assessments of HAL's capability to reverse engineer or to apply technologies from other projects, such as the work performed for the Folland Gnat.[15] HAL is claimed to have struggled to convince both the IAF and MoD that the design of the Marut was acceptable; much attention was given to the unacceptably high level of trail drag that the airframe produced, as well as dissatisfaction with the Marut's speed and manoeuvrability, both of which were below IAF standards upon its introduction.[12]

Kurt himself had a major influence on the project, and accordingly of its shortcomings. While working on the Marut, Kurt has been credited with having instructed his fellow engineers well during the project, but was also noted for his rigid stance on aspects of the design.[16] He typically had little interest in lobbying the Indian government for funding refinements to the design; elements of the IAF have been alleged to have held dismissive attitudes toward Kurt and of his abilities, rarely coordinated with him on issues with the aircraft, which in turn exacerbated the type's performance issues.[15] The level of technological transfer between Germany and India on the project was subject to criticism as well.[17]

According to author Satish Kumar, the limited technological capabilities of the Indian aerospace industry had created a heavy reliance on foreign technologies and imported components.[2] Kumar also attributes HAL's willingness to undertake overly-ambitious defence projects as being partially responsible for the project's outcome and the Marut's performance.[2] Author Amit Gupta observed that the Marut was not only heavily dependent on foreign-sourced materials, but that it was more expensive to manufacture the type in India than to have imported completed aircraft.[3] The level of indigenous components increased over time, reportedly having reached 70 per cent by December 1973.[5] The allocation of scarce resources to reproducing components that could have been readily acquired externally represented a high level of opportunity cost to India. According to Swarna Rajagopalan, India lacked the infrastructure and scientific base to successfully produce an effective indigenous combat aircraft at that time.[6]

A preserved Marut on static display. This aircraft had participated in the Battle of Longewala.

The Marut was used in combat in a ground attack role, where its safety features such as manual controls whenever the hydraulic systems failed, and twin engines, increased survivability. According to aviation author Pushpindar Singh, the Marut had excellent low-level flying characteristics, but its maneuverability suffered due to the lack of engine power, maintenance issues also resulted in the type being problematic in service.[5]

In 1967, a single Marut was used as a testbed for the Egyptian indigenously-developed Brandner E-300 engine.[19] The Indian team was recalled in July 1969, while the Egypt-based Marut was abandoned.[5]

Given the limited number of Marut units, most Marut squadrons were considerably over-strength for the duration of their lives. According to Brian de Magray, at peak strength No.10 Squadron had on charge 32 Maruts, although the squadron probably did not hold a unit-establishment of more than 16. The Marut squadrons participated in the 1971 war and none were lost in air-to-air combat, although four were lost to ground fire, and two were destroyed on the ground. Three Marut pilots were awarded the Vir Chakra commendation.[20]

Maruts constantly found themselves under heavy and concentrated fire from the ground during their low-level attack missions. On at least three occasions, Maruts regained their base after one engine had been lost to ground fire. On one of these, a Marut returned to base without escort on one engine, from about 150 mi (240 km) inside hostile territory. On another occasion, a pilot flying |his Marut through debris that erupted into the air as he strafed a convoy felt a heavy blow to the rear fuselage of the aircraft, the engine damage warning lights immediately glowed, and one engine cut out. Fortunately, the Marut attained a safe and reasonable recovery speed on one engine. Consequently, the pilot had no difficulty in flying his crippled fighter back to base. Another safety factor was the automatic reversion to manual control in the event of a failure in the hydraulic flying control system, and there were several instances of Maruts being flown back from a sortie manually. The Marut had a good survivability record in enemy airspace.[21]

In the Indo-Pakistani War of 1971, some Maruts and Hawker Hunter aircraft were used to give close support to an Indian border post in the decisive Battle of Longewala, on the morning of 5 December 1971. The aerial attack was credited with destroying a large number of tanks that had been deployed by Pakistani ground forces.[22] More than 300 combat sorties were flown by the Maruts during a two-week period in the war.[5]

One aerial kill was recorded as having been achieved by a Marut; on 7 December 1971, Squadron Leader KK Bakshi of No. 220 Squadron shot down a PAF F-86 Sabre, (reportedly flown by Flag Officer Hamid Khwaja of No. 15 Squadron of the Pakistan Air Force).[23] Reportedly, not a single Marut sustained damage or a loss due to enemy aircraft.[5]

By 1982, the IAF was proposing that that Marut fleet be phased out on the basis that the type was "no longer operationally viable".[5] Supporters such as Air Commodore Jasjit Singh pointed out that the type had performed well in the 1971 combat, and had enjoyed superior safety records to other IAF aircraft such as the Gnat. Some aircraft had less than 100 recorded flight hours when the retirement of the Marut was being mooted.[5]